This invention is directed to heading determination and, more particularly, to the determination of the heading of a vehicle.
In the past, a variety of devices for providing information related to the heading of a vehicle have been proposed and used. The most common of these devices is a simple compass that, as is well known, provides heading information by relating a needle in alignment with the earth's magnetic field to a compass card. While such devices are adequate to provide a general indication of direction, they are relatively inaccurate. The primary reason they are inaccurate is that the earth's magnetic field has distortions (magnetic anomalies) in localized areas due to magnetizable materials such as bridges, pipelines, etc. These magnetic anomalies distort the localized earth's magnetic field whereby the compass direction indication is distorted.
As an alternative to a magnetic compass, relatively sophisticated gyroscopic indicators have been proposed for use in many vehicles, particularly aircraft and large ocean going vessels. While such sophisticated devices overcome some of the above noted problems of magnetic compasses, they are obviously expensive and, therefore, not suitable for widespread use.
In recent years, attempts have been made to develop vehicle location monitoring systems that provide an indication of the location of vehicles in a predetermined area. For example, attempts have been made to provide vehicle location monitoring systems for monitoring the location of police vehicles on the streets of a city. Some of these systems utilize the principles of dead reckoning and require accurate, relatively inexpensive, heading sensors. Obviously, while inexpensive, compass systems do not provide the necessary accuracy. And, gyroscopic type systems are more expensive than desirable.
In an attempt to overcome some of the foregoing problems, sophisticated, but uncomplicated, magnetic devices have been proposed. One such device is described in U.S. Pat. No. 3,895,869 entitled "Heading Sensor with Compensation Windings" issued to Richard W. Lewis. While the device described in that patent overcomes many of the disadvantages of prior art magnetic compasses, certain disadvantages remain. More specifically, while magnetic information of the type generated by the invention described in the foregoing patent is accurate when averaged over long distances, it is not as accurate as desirable over short distances, particularly in areas where the localized earth's magnetic field is distorted. The present invention is primarily directed to overcoming this disadvantage of an entirely magnetic vehicle heading system.
Therefore, it is an object of this invention to provide a new and improved vehicle heading system.
It is also an object of this invention to provide a compensated vehicle heading system.
It is a further object of this invention to provide a new and improved vehicle heading system suitable for use in vehicle location monitoring systems.
It is another object of this invention to provide a new and improved vehicle heading system that has excellent accuracy, yet is low in cost.